Underlord + Lion

Why this works

Trying to lock down a single target is where this pair finds some common ground. Underlord can cast Pit of Malice over an area, and any enemy caught in it becomes an easy target for Lion’s Earth Spike and Hex. The long duration of the root makes it forgiving for Lion to land his spells, creating a straightforward disable chain that can secure a pick-off. This is most effective during ganks or early teamfights when isolating one enemy hero is the main goal. Underlord’s Firestorm can be layered on top to add significant damage while the target is held in place.

The synergy tends to fall off as the game goes on. While their initial lockdown is fine, their larger teamfight goals don't align perfectly. Lion wants to quickly burst a key hero with Finger of Death and retreat, while Underlord wants to establish a frontline position and force a long, drawn-out fight within his spells. Fiend's Gate also has very little direct interaction with what Lion wants to do. So, they can set each other up for a kill, but they don't fundamentally solve each other's problems or create a cohesive teamfight plan on their own.